Hack-charging on a generator

[Cottonwood]

For curious TMC members (like me) that don't wanna look it up (unlike me):
Honda EU2000i - MSRP US $1149.95

The "EU20i" appears to be a variant for other markets.

I already had a Honda EU2000i for other reasons. I fired it up and gave it a try with the UMC and the 5-15 plug. It did not work! The green light came on for a moment, then the red light came on declaring a fault. Has anyone actually run an S UMC off of a Honda EU2000i?

BTW, this was just a fun experiment. There are too many 5-15's out there in the wild to carry something like this around, but the generator fits perfectly in the Frunk. :biggrin:

 

[FlasherZ]

I already had a Honda EU2000i for other reasons. I fired it up and gave it a try with the UMC and the 5-15 plug. It did not work! The green light came on for a moment, then the red light came on declaring a fault. Has anyone actually run an S UMC off of a Honda EU2000i?

I have.

You are seeing a ground fault (red light). The Model S expects to see a voltage between the hot and ground. Honda's EU series generators leave the power "floating" and do not bond ground to neutral, as a result you get no voltage between ground and hot and the UMC complains. This is easily solved by creating a "dummy plug" - made using a standard 120V 3-prong plug - that connects ground to neutral (the larger blade in the receptacle, or the silver screw) and plug it into the other socket on the EU2000i.

(This is true for other generator sets as well that do not bond ground and neutral -- in any system, ground and neutral should be bonded in only ONE place, and generator manufacturers purposely leave it float because of an assumption that ground is bonded somewhere else -- say, in the service disconnect panel of a home. At a job site, though, where the generator is the only source, you want it bonded and you want to drive a grounding electrode connected to the generator's frame as well.)

 

[4sevens.com]

I have.

You are seeing a ground fault (red light). The Model S expects to see a voltage between the hot and ground. Honda's EU series generators leave the power "floating" and do not bond ground to neutral, as a result you get no voltage between ground and hot and the UMC complains. This is easily solved by creating a "dummy plug" - made using a standard 120V 3-prong plug - that connects ground to neutral (the larger blade in the receptacle, or the silver screw) and plug it into the other socket on the EU2000i.

(This is true for other generator sets as well that do not bond ground and neutral -- in any system, ground and neutral should be bonded in only ONE place, and generator manufacturers purposely leave it float because of an assumption that ground is bonded somewhere else -- say, in the service disconnect panel of a home. At a job site, though, where the generator is the only source, you want it bonded and you want to drive a grounding electrode connected to the generator's frame as well.)

So you just have a special cable that shorts the larger placed to the ground? That doesn't sound very safe. Are you sure?

Also have you tried using two of those generators with a special device that bridges them for 120v and 30A?

 

[TonyWilliams]

Many times, the "briefcase" generators like Honda and Yamaha won't charge an electric car if the EVSE can't sense a ground. With a simple plug in any outlet of the generator wired to have a teeny, tiny path of current from hot to ground, this will enable the generator to sense ground, and therefore charge the car.

The easy way to make this work is take a NEMA 5-15P plug and install two 1/2 watt 100k ohm resistors. One from neutral to ground (usually green), and the other from hot to ground. Then simply plug this into any outlet on the generator, and your EVSE into the other outlet. This will safely pass the ground detect on the EVSE, while not being a hazard in any other way.

If charging from a 240 volt generator, connect both hot legs and the neutral to ground. Then earth is then properly floating in the "middle".

 

[FlasherZ]

So you just have a special cable that shorts the larger placed to the ground? That doesn't sound very safe. Are you sure?

Also have you tried using two of those generators with a special device that bridges them for 120v and 30A?

Yes, when you have an isolated generation facility, you need to bond neutral to ground in ONE place. Neutral should be grounded. When you're completely isolated, as with a generator, the safest installation connects 1 grounding electrode driven 6 feet into the ground to the chassis of the generator, then the neutral is bonded to that as well.

The plug I have generates the bonding (just ties neutral to ground) for those generators that don't have a bonding jumper or setting.

What's bad - and the reason the generators don't do this by default - is when that bonding occurs in multiple places, which can create a ground loop through a human.

- - - Updated - - -

The easy way to make this work is take a NEMA 5-15P plug and install two 1/2 watt 100k ohm resistors. One from neutral to ground (usually green), and the other from hot to ground. Then simply plug this into any outlet on the generator, and your EVSE into the other outlet. This will safely pass the ground detect on the EVSE, while not being a hazard in any other way.

There is no need for that resistor. The Tesla EVSE checks for potential from hot to ground by generating its own leakage path, it doesn't need current leakage. All you need to do is properly bond the neutral and ground (and as mentioned, it's a good idea to use a grounding rod if you can, for safety's sake).

 

[efusco]

I'm having a difficult time understanding exactly what is being grounded to what to make this work. I'd love to be able to use my gennie as an emergency back up, but also got the red warning when I tried. There is a nice ground wire from the main generator, but it sounds like I need another separate ground... can someone take a photo or diagram this or something? I just can't get a picture of what exactly needs to be done.

 

[Cottonwood]

You are seeing a ground fault (red light). The Model S expects to see a voltage between the hot and ground. Honda's EU series generators leave the power "floating" and do not bond ground to neutral, as a result you get no voltage between ground and hot and the UMC complains. This is easily solved by creating a "dummy plug" - made using a standard 120V 3-prong plug - that connects ground to neutral (the larger blade in the receptacle, or the silver screw) and plug it into the other socket on the EU2000i.

The fault that I am seeing is four flashes of the red light which thehttps://Mobile Connector Owner's Manual says is "Ground Lost." Plugged into a 5-15 of my home, this fault does not occur. This is all consistent with your description above.

Based on this, I made a plug as you described, and gave it a try. The picture below shows my shorting plug with a labeled picture of a 5-20 receptacle. As you can see, ground (green) is connected to neutral (silver).

With this plugged into the Honda EU2000i and the Mobile Connector plugged into the other receptacle, I still got the 4-flashes, "Ground Lost" fault.

Just to try everything, I took an old extension cord that I had repaired years ago, opened up the back of its receptacle, and shorted ground to neutral, and plugged the mobile connector to the Honda with the modified extension cord in series. No joy; I still got the dreaded 4-flashes fault.

Thoughts?

I have a relatively early mobile connector. I've now spent far too much time on something that I will rarely, if ever, use. BTW, I looked up the fuel consumption for this Honda at this power; its about 4 hours/gal. With a charge rate of 3 mph, that give this charging method a mileage of 12 mpg!

 

[FlasherZ]

Just to try everything, I took an old extension cord that I had repaired years ago, opened up the back of its receptacle, and shorted ground to neutral, and plugged the mobile connector to the Honda with the modified extension cord in series. No joy; I still got the dreaded 4-flashes fault.

Thoughts?

I have a relatively early mobile connector. I've now spent far too much time on something that I will rarely, if ever, use. BTW, I looked up the fuel consumption for this Honda at this power; its about 4 hours/gal. With a charge rate of 3 mph, that give this charging method a mileage of 12 mpg!

First, just as a side note, I calculated my Tesla gets the equivalent of 17 MPG when charging using the 25 kW Generac whole-house generator (based on spot prices of gallons-of-propane to gallons-of-gasoline) when charging the Tesla.

If you have a voltmeter handy, when the generator is running, take measurements of hot vs. neutral, hot vs. ground, and neutral vs. ground both with and without that plug.

As the UMC and vehicle itself have no ground reference to check (the UMC isn't forced to sit on the ground and the car sits insulated on its tires), the only thing the UMC can do is check that there is voltage between line and ground. You might try driving a piece of wire about a foot into the ground and connecting it to the G terminal on the generator, just to truly ground the chassis, although I don't know how that could be making a difference.

It worked for me, but maybe your revision of generator is different somehow. I've read of other issues trying to use these generators with anything that does ground fault checking, but in most cases the bonding works.

 

[andrewket]

First, just as a side note, I calculated my Tesla gets the equivalent of 17 MPG when charging using the 25 kW Generac whole-house generator (based on spot prices of gallons-of-propane to gallons-of-gasoline) when charging the Tesla..

I've got a 20kW Cummins Onan natural gas generator. I specifically kept the HPWC and my volt evse off the generator because I thought it would be very inefficient and most power outages are measured in hours. Having said that, there is a minimum amount of gas the generator will use not under load (idle). I've often wondered how much electricity I might be "throwing away" when this occurs. We had one outage that did last almost 3 days. The generator ran the entire time. Over night, when the a/c wasn't running, the generator had almost no load. If I could charge the car, even at 6-12A without increasing natural gas consumption, from a marginal cost perspective it's free.

Any idea how much current these generators create at "idle"?

A

 

[FlasherZ]

Any idea how much current these generators create at "idle"?

They really don't create any at "idle". Any current draw whatsoever creates physical resistance in the turbine and causes the engine to burn more fuel. When there is no load, there is a minimum amount of fuel required to keep the turbine spinning. Any load you add will have a net addition to your fuel consumption.

That said, I know where you're going -- it is less expensive on a per-unit basis to run a generator at a higher load. At 25% load, my generator burns 2.4 gals of propane per hour, while at 100% load, my generator burns 4.72 gals of propane per hour. On a per-amp basis, running it at 25% load consumes 0.09 gallons per amp per hour while running it at full load consumes 0.045 gallons per amp per hour -- half the cost per amp.

It will always be additive to your fuel consumption, though - so to do a proper comparison, you really have to factor how the car will be charged otherwise - and it's usually far more cost-effective to do it off the grid (or perhaps even in your Volt's case with its own generator engine).

 

[strider]

So you just have a special cable that shorts the larger placed to the ground? That doesn't sound very safe. Are you sure?

Also have you tried using two of those generators with a special device that bridges them for 120v and 30A?

IIRC the UMC will only charge at 12A as it assumes a 5-15. The Roadster will let you go up to 16A if you're plugged into a 5-20 (honor system though). So increasing amperage will not give you higher charge rates at 120V.

 

[cinergi]

IIRC the UMC will only charge at 12A as it assumes a 5-15. The Roadster will let you go up to 16A if you're plugged into a 5-20 (honor system though). So increasing amperage will not give you higher charge rates at 120V.

Both Roadster and Model S have a NEMA 5-20 plug option for properly achieving 16 amps from a 20 amp 120v outlet.

 

[strider]

Both Roadster and Model S have a NEMA 5-20 plug option for properly achieving 16 amps from a 20 amp 120v outlet.

I stand corrected. Still, 16A is the max current the car will pull on a 120V circuit so ganging 2 gensets together to create a "TT-30" won't buy you a full 120V/24A rate.

 

[FlasherZ]

I stand corrected. Still, 16A is the max current the car will pull on a 120V circuit so ganging 2 gensets together to create a "TT-30" won't buy you a full 120V/24A rate.

If you use an adapter, the Model S can charge up to 20A @ 120V. The software limits the rate to 20A when it sees ~120V. You can make this work by using a special adapter, if you have to.

 

[cinergi]

If you use an adapter, the Model S can charge up to 20A @ 120V. The software limits the rate to 20A when it sees ~120V. You can make this work by using a special adapter, if you have to.

? With their 5-20 adapter it would pull a max of 16, or are you talking about concocting your own adapter that sends a 20+ pilot?

 

[FlasherZ]

? With their 5-20 adapter it would pull a max of 16, or are you talking about concocting your own adapter that sends a 20+ pilot?

I have a specially configured TT-30 to 14-30 adapter.

 

[efusco]

I have a specially configured TT-30 to 14-30 adapter.

Can you diagram that, or show a photo of how you've done that? Here's what I want to charge with on my generator. I have a cord adapter and can connect my UMC, but I get the blinking red ground error. Teach me swami!

 

[FlasherZ]

Can you diagram that, or show a photo of how you've done that? Here's what I want to charge with on my generator. I have a cord adapter and can connect my UMC, but I get the blinking red ground error. Teach me swami!

Well, two things -- first, what type of generator is this? The car really dislikes the smaller standard-type generators as they don't really generate sufficiently clean power. You will likely not get the car to remain charging for periods of time from that type of generator.

If you'd like to try, you will need to bond ground to neutral on that generator. On some models (see your owner's manual) there is a bonding jumper you can install. On others, you'll have to accomplish it in other means. One option you have is doing it on the L14-30 plug itself. The ground pin is the one with the hook and the neutral is directly opposite it (the two hots are directly adjacent to ground). Another option is to do what I mentioned up the thread, take a simple 5-15 plug, jumper the neutral to ground, and plug it into one of the 110 sockets on the generator.

You'll obviously need an L14-30 adapter of some sort to one of the receptacles the Tesla can use. Your best bet is an L14-30P to 14-30R adapter if you have the Tesla 14-30 UMC adapter, or you can wire an L14-30P to 14-50R adapter if you want to use the 14-50 you have (all standard disclaimers apply).

 

[hughconn]

New Whole house nat gas Kohler generator coming in 2 weeks, along with the new 14-50 Nema outlet. Model S comes two weeks later. Electrician says no problem charging the Tesla when the generator is running. As long as we don't lose gas, I should be covered.

 

[Lloyd]

or you can wire an L14-30P to 14-50R adapter if you want to use the 14-50 you have (all standard disclaimers apply).

I found that adapter already made up for a reasonable price. HERE